a. Field of the Invention
The invention relates generally to electroplating equipment and, more particularly, to apparatus for spray electroplating of selected areas of a workpiece. The preferred field of application is in the production of solid-state devices and microcircuits where the invention may be used, in particular, for the application of gold or other noble metals onto contact pads of a semiconductor body or clipped strips to provide for stable low resistance in these areas, which is not affected by the environment.
B. Description of the Prior Art
In spray plating, a workpiece connected to the negative pole of a voltage source is continuously sprayed with a plating solution, the areas not to be plated from the action of this solution having been insulated in advance. Ions of metal in the plating solution, positively charged as a result of the contact of the plating solution with the anode, are deposited on the surface of the workpiece.
Attempts to enhance the efficiency of the above process by feeding the workpieces continuously into the plating zone are opposed by the necessity of insulating the workpieces locally from the electrolyte, which requires firm engagement between the workpieces and insulating gaskets throughout the plating process.
Conventional conveyor-type apparatus for selective electroplating, which make it possible to reduce the time wasted on repositioning an elongated workpiece when treating different areas of its surface, have not found extensive application in plating with noble metals because of the irreparable losses of plating solution inevitable during the advance of a freshly plated workpiece, and also because of the relatively high cost stemming from their complicated and metal-consuming construction.
There is known in the art an apparatus for selectively and simultaneously electroplating a plurality of areas of a workpiece, as disclosed in the British Pat. No. 1393138. This apparatus comprises a plating unit, the cavity of which communicates with a plating solution feed system and the top wall of which serves as a workpiece supporting member, and means for pressing a workpiece and the supporting member together, which is movably mounted above the plating unit and operatively connected with a vertical movement mechanism such as a fluid cylinder.
Mounted on the external surface of the top wall of the plating unit are means masking the workpiece surface areas not to be plated and means for orienting the workpiece. There is a sealing gasket on the bottom external surface of the pressing means. The apparatus comprises an anode mounted in the path of the plating solution flow, as it is fed towards the workpiece, and a plurality of nozzles in the plating unit, through which the plating solution is sprayed onto the workpiece. The workpiece functions as the cathode of the apparatus. The upper wall of the plating unit has ports for access of plating solution to the exposed areas of the underside of the workpiece to be plated.
Workpieces placed on the masking means of the plating unit are pressed against the masking member by the sealing gaskets of the pressing means when the pressing means is in the lowered position.
Thus, the pressing means of the above machine performs the sealing function only, and as the workpiece orientation means are mounted on the stationary top wall of the plating unit directly under the pressing means, it is impossible to change workpieces before plating is completed and the pressing means is retracted into the raised position.